Nitranium perchlorate reaction rate alteration

ABSTRACT

The rate of thermal decomposition of certain high energy solid state materials, such as nitronium oxidizers, may be either increased or decreased by doping to replace ions in the structure with ions having a different valence. Decompsoition rate is increased if univalent anions are replaced with multivalent anions, and rate is conversely decreased if univalent cations are replaced with multivalent cations that are less colored than the host material.

United States Patent Maycock et al. Nov. 6, 1973 [54] NITRANIUMPERCHLORATE REACTION 3,167,386 1/1965 McElroy et al. 23/85 X RATEALTERATION 3,186,790 6/1965 Brovvn et a1. 23/85 X 2,190,703 2/1940 Davis149/76 X [75] Invent rs: John Norman May m r 3,172,793 3/1965 Markowitz1 149/19 Md.; Louis Witten, Cincinnati, Ohio 3,418,183 12/1968 Rice149/6 [73] Assignee: Martin Marietta Corporation, New OTHER PUBLICATIONSYork Verneker eta1., .1. Inorganic NucL. Chem., Vol. 29, pp. [22] Filed:Nov. 20, 1969 2729-2730 (1967).

[21] Appl' 878591 Primary ExaminerCar1 D. Quarforth Related US.Application Data Assistant Examiner-E. A. Miller [63]Continuation-in-part of Ser. No. 589,185, Oct. 19, n ym B- EiSel an GayChin 1966. 52 U S Cl 149/74 149/75 149/76 [57] ABSTRACT 1 The rate ofthermal decom osition of certain high en- 423/386 P [51] Int CL C06b11/00 ergy solid state materials, such as nitronium oxidizers, [53]Field 49/76 74 may be either increased or decreased by doping to replaceions in the structure with ions having a different valence.Decompsoition rate is increased if univalent [56] References Citedanions are replaced with multivalent anions, and rate is converselydecreased if univalent cations are replaced UNITED STATES PATENTS withmultivalent cations that are less colored than the 1,284,328 15/1913lbs/1e gueur host i L 3,l47,l 196 c rone 3,269,879 8/1966 Stammlcr et a1149/2 10 Claims, N0 Drawings NlTlRANllUM PERCHLORATE REACTllON RATEALTERATION This application is a continuation-in-part of our copendingapplication, Ser. No. 589,185, filed Oct. 19, 1966.

This invention relates to methods of altering the chemical reactionrates of materials, and to new materials obtained by such methods. Moreparticularly, it relates to methods for altering the structure ofexisting high energy materials so that their chemical reaction rates maybe either increased or decreased as desired. High energy materials forthe purposes of this discussion are those that under appropriateconditions undergo substantial exoenergetic, usually exothermic,reactions. These include explosives, fuels, and propellant oxidizers.

The desirability of modifying the chemical reaction rates of suchmaterials has long been recognized. Various applications of military andcommercial explosives require different explosive characteristics andfor years the chemical reaction rates of explosives have been adjustedto provide these characteristics. Reaction rate alterations have alsobeen performed to render a high energy material suitable for entirelydifferent applications. For instance, the chemical reaction rates ofmaterials generally used as explosives have been slowed to creatematerials suitable for rocket propellants. The chemical reaction ratesof both explosives and oxidizers have been both increased and decreased.

Prior art modifications of the chemical reaction rates of high energymaterials generally suffer from one or more limitations. Suchmodification has been usually accomplished by mechanical mixing of anadditional ingredient or ingredients with the high energy materials.Such mixing has disadvantages. The additional in gredient, whileproviding the desired chemical reaction rate, may affect othercharacteristics of the material unfavorably. Also, high energy materialsare often combined with binders and the like to form charges, or forother purposes, and the additives for altering reaction rates oftenreact disadvantageously with these other materials. A trade-off musttherefore be made between the advantages of reaction rate change and theconcomitant degradation of other desirable characteristics. Further, itis difficult in such mechanical mixing to achieve the ultimate inuniform dispersion, and uneven reactions often result from theconsequent inhomogeneity.

Prior art methods of modifying chemical reaction rates are generallyquite specific: usually a particular additive will work with only one ora small, closely related group, of high energy materials. No overallapproach has been developed that is usable for all or a large group ofhigh energy materials, and that will permit the reaction rate to beincreased or decreased,

whichever is desired. I

It is an object of this invention to provide a method of altering thechemical reaction rate of a large group of solid materials, includingmany high energy materials.

it is a further object of this invention to provide such a method thatwill permit the chemical reaction rate to be either increased ordecreased, as desired, and that will result in smooth and evenreactions.

it is still another object of this invention to provide certain highenergy materials that have more desirable chemical reaction rates as aresult of modification by this method.

We have discovered a method for altering the chemical reaction rate of asolid material containing point defects which is rich in at least onegaseous element and capable of thermally decomposing into completelygaseous products. Solid materials containing point defects include bothmaterials in which the bonding is purely ionic and materials, such aslead. azide, in which the bond is partly covalent and partly ionic.

These materials are comprised of anions and cations held in a regularlattice structure by ionic bonds or by a combination of ionic andcovalent bonding. The materials that are amenable to the process of thisinvention may not all be normally considered as crystals when the wordis used in its loose sense to describe a material having crystallinestructure on a macro scale. Rather, the crystalline structure referredto is the basic structure of the material, and may exist only on a microscale, as, for instance, when the material is powdered.

The point defects contained in these solids are ion vacancies; that is,positions in the crystalline structure that would normally be occupiedby an anion or cation but which are in fact vacant. Such ion vacanciesbear an effective charge of a polarity opposite to that of the ion thatwould occupy that site if the lattice structure were regular, orperfect. A cation vacancy would accordingly have an effective negativecharge and an anion vacancy, an effective positive charge.

The chemical reactions of such materials may be complex in nature andthe overall reaction may include a series of individual reactions.However, all chemical reactions of solids containing point defects arecharacterized by the loss of electrons by the anions, these electronsbeing subsequently captured by the vacant lattice sites that are createdby anion vacancies and that form effective positive charges. The greaterthe number of anion vacancies in the material, the faster the rate ofelectron capture and the faster the rate of chemical reaction.

The chemical reaction rate may be increased by increasing the number ofanion vacancies in the solid, or by decreasing the number of cationvacancies. An increase in the number of cation vacancies, or a decreasein the number of anion vacancies, will tend to slow down the chemicalreaction and decrease the reaction rate.

The number of lattice site vacancies (point defects) may be adjusted byreplacing some of the ions with ions having the same polarity but adifferent valence. Consider a solid composed of univalent anions andunivalent cations. Suppose it is desired to increase the chemicalreaction rate of the solid. As described above, this may be accomplishedby increasing the number of anion lattice site vacancies. To do this, wereplace some of the univalent anions in the lattice structure withanions having a greater valence, say divalent anions. Since the solidmust remain electrically neutral, the additional charge incorporated bythe divalent anions will be balanced by the loss of univalent anions;

that is, by an increase in the number of anion vacancies in the lattice.

If some of the univalent cations are replaced with divalent cations thatare less colored than the host material, that is, that absorb light atwavelengths shorter than the wavelengths at which the host materialabsorbs light, the number of cation vacancies increases and the chemicalreaction rate is decreased.

Obviously, we are not limited to replacing univalent ions with divalentions in order to alter the number of lattice site vacancies, althoughthis type of substitution would be probably the most used. Univalentions could also be replaced by ions having a valence greater than two.Also, in a solid composed of ions having a valence greater than one,some of the ions could be replaced by ions having a lower valence. Thislatter replacement would generally have an opposite effect on thereaction rate than replacement with ions having a greater valence. lfdivalent anions were replaced with univalent anions that are lesscolored than the host material, that is, that absorb light atwavelengths less than the wavelength at which the host material absorbslight, the number of anion vacancies would decrease, and the reactionrate would also decrease. And if divalent cations were replaced withunivalent cations, the number of cation vacancies would decrease, andthe reaction rate would increase.

in order to effect the ion replacement described, the original solid anda material containing the replacement ions may both be dissolved in asuitable solvent. Crystals obtained from the solution, as by cooling it,will then have the desired characteristics. The following examplesdescribe in detail the operation of the process.

EXAMPLE 1 The chemical reaction rate of nitronium perchlorate (NO ClOwas decreased by the substitution of divalent strontium cations (Sr forthe univalent nitronium cations (NOJ) on approximately a 10' mole ratio.Ten grams of nitronium perchlorate (NO ClO and 100 milligrams ofstrontium chloride (SrCl were placed in 10 milliliters of undilutednitric acid (HN at room temperature. The solution temperature was raisedto 70C., at which point all of the solids were dissolved in thesolution. The solution was then permitted to cool to room temperature.The crystals that had precipitated were filtered off and dried for about24 hours under a vacuum of about mm of H The-chemical reaction rate ofthe crystals obtained bythis process was compared with the reaction rateof pure nitronium perchlorate crystals by comparing the relative periodsof time required for the pressure of oxygen (O evolved from thermaldecomposition to cover a specified pressure range when the materialsthermally decomposed at a constant temperature and in a closed volumecontainer. When the same weight of both materials was thermallydecomposed in a closed volume of 1.3 liters at a constant temperature of80C., it required 1.2 minutes for the oxygen pressure resulting frompure nitronium perchlorate crystal decomposition to go from 0.01 p. to0.25 while it required 7.5 minutes for the oxygen pressure from thermaldecomposition of the crystals produced by this process to cover the samerange under the same conditions.

EXAMPLE 2 The chemical reaction rate of nitronium perchlorate (NO CIOwas decreased by substituting divalent cations of calcium (Ca*") for theunivalent cations of nitronium (NO on approximately a l0- mole ratio.The process was identical to that described in Example 1 except that 113milligrams of calcium nitrate (Ca(- N09 was substituted for thestrontium chloride of Example 1.

The rate of thermal decomposition of the resulting crystals was comparedto the thermal decomposition rate of pure nitronium perchlorate crystalsin the same manner as in Example 1. At a constant temperature of 120C.and in a closed volume of 2.2 liters, 4.5 minutes were required for theoxygen (0 pressure resulting from the pure nitronium perchloratedecomposition to increase from 15 p. to 40 ;1., whereas 6.7 minutes wererequired to cover the same pressure range under the same conditions bythe oxygen (0 evolved from decomposition of the crystals obtained fromthe process of this example. For the pressure range of p. to 300 ,2,under the same conditions, 5.2 minutes were required by the oxygen (0evolved from pure nitronium perchlorate and H2 minutes for the oxygen (0evolved from the crystals of the process of this example.

EXAMPLE 3 The chemical reaction rate of nitronium perchlorate (NO CIOwas increased by the substitution of divalent sulfate anions ($0 for theunivalent perchlorate anions (ClOf) on approximately a 10 mole ratio.The process was identical to that of Examples 1 and 2 except that 91milligrams of ammonium sulfate ((NH SO,,) was mixed with the 10 grams ofnitronium perchlorate (NO ClO in the 10 milliliters of undiluted nitricacid (HNO The rate of thermal decomposition of the crystals obtained bythe process of this example was compared with the decomposition rate ofpure nitronium perchlorate crystals in a manner similar to that ofExamples 1 and 2. At the same constant temperature and in the sameclosed volume as in Example 2 (C. and 2.2 liters, respectively), theoxygen (0 evolved from the pure nitronium perchlorate crystals required(as in Example 2) 4.5 minutes to increase in pressure from 15 p. to 40p. and 5.2 minutes to increase from 100 p. to 300 u. The oxygen evolvedfrom the decomposition of the crystals produced by the process of thisexample, however, required only 3.0 minutes to increase in pressure from15 y. to 40 IL and only 3.5 minutes to increase from 100 p. to 300 u.

EXAMPLE 4 The chemical reaction rate of ammonium perchlorate (NH ClO wasreduced by substituting divalent cations of calcium (Ca**) for theunivalent cations of ammonium (NI-l on approximately a 10 mole ratio.Ten grams of ammonium perchlorate (NH ClO,) and 100 milligrams ofcalcium nitrate (Ca(NO were placed in 25 milliliters of distilled waterat room temperature. the temperature of the solution was raised to 90C.,at which point all of the solids were dissolved in the solution. Thesolution was then permitted to cool to room temperature. The crystalsthat had precipitated were filtered off and dried for about 24 hoursunder a vacuum of about 10 mm of H After vacuum drying, the crystalswere heated in an oven maintained at between 1 l0l 30C. for about fourhours to remove any remaining water.

The rate of decomposition of the resulting crystals was compared to therate of decomposition of pure ammonium perchlorate (NH ClO crystals asin the previous examples, by comparing the length of time required foroxygen (0 evolved during decomposition to cover a prescribed range ofpressures while maintained at a constant temperature. The decompositionrate is of course a function of temperatures, and these comparisons werecarried out at a number of temperatures. The results of the comparisonsfor two temperatures are set forth in the following table:

Pressure Time for 0 Time for 0 from Pure from Crystals Temp. (C.) Range([1.) NH ClO of this Process 225 50 to 100 min. 24 min. 250 50 to 100 2min. 4 min.

Where the chemical reaction rate comprises thermal decomposition, thesubstituted ion should be thermally stable at the temperature of thermaldecomposition of the original material.

While other methods of effecting the substitution of the desired ioninto the lattice structure are of course possible and within thecontemplation of our invention, the general procedure used in thepreceding examples is a convenient one. When, in accordance with thisprocedure, the replacement ion forms part of a salt that is dissolved ina common solvent along with the original material, it is desirable tomake sure that the other ion with which the replacement ion is combinedto form the salt does not operate to destroy the effect created by thedesired replacement. For instance, consider an original materialcomprised of univalent ions A B', with the reaction rate to be decreasedby replacing the A ion with X. if the X ion is to be substituted bydissolving A03 and X Y salts in a common solvent, then the resultingcrystalline material might also have Y ions substituted for B ions,which would tend to vitiate or cancel out the decrease in reaction rateintended to be accomplished by substituting the X divalent cation for Aunivalent cation. Therefore, in performing a cation substitution by thismethod, it would be well either to use a salt of the form X (Z) with aunivalent anion coupled with the divalent cation, or, if a divalentanion Y- is to be used, make sure that it is not compatible with the AERcrystalline structure and therefore will not be substituted in thelattice for B" anions.

As the above description and examples make clear, we have discovered anew and powerful method for varying at will the chemical reaction ratesof those solid materials having point defects, and new and usefulmaterials formed by this process. Various modifications that will beobvious to those skilled in the art are within the contemplated scope ofour invention, which is limited only by the appended claims.

We claim:

it. A process for accelerating the rate of thermal decomposition ofnitronium perchlorate comprising cocrystallizing with it about 0.001 toabout mole percent of a foreign anion that is thermally stable at thetemperature of decomposition of said nitronium perchlorate and that hasa valence state greater than one, and a corresponding amount of a cationhaving a valence less than the valence of said. anion.

2. The process of claim 1 wherein said anion is $0,. 3. A process fordecelerating the rate of thermal decomposition of nitronium perchloratecomprising cocrystallizing with it about 0.001 to about 20 mole percentof a foreign cation that a. has a valence state greater than one, b. isthermally stable at the temperature of decomposition of said nitroniumperchlorate, and c. does not absorb light at a wavelength shorter thanthe wavelength at which nitronium perchlorate absorbs light, and thecorresponding amount of an anion that a. has a valence state less thanthe valence state of said cation, and b. does not absorb light at awavelength shorter than the wavelength at which nitronium perchlorateabsorbs light. 4. The process of claim 3 wherein said cation is Ca. 5.The process of claim 3 wherein said cation is Sr. 6. The novelcomposition of matter comprising a nitronium perchlorate lattice having;in ionic distribution therein about 0.001 to about 20 mole percent of aforeign anion that is thermally stable at the temperature ofdecomposition of said nitronium perchlorate and that has a valence stategreater than one, and a corresponding amount of a cation having avalence less than the valence of said anion.

7. The novel composition of matter of claim 6 wherein said anion is 8.The novel composition of matter comprising a nitronium perchloratelattice having in ionic distribution therein about 0.001 to about 20mole percent of a foreign cation that a. has a valence state greaterthan one, b. is thermally stable at the temperature of decomposition ofsaid nitronium perchlorate, and c. does not absorb light at a wavelengthshorter than the wavelength at which nitronium perchlorate absorbslight, and the corresponding amount of an anion that a. has a valencestate less than the valence state of said cation, and b. does not absorblight at a wavelength shorter than the wavelength at which nitroniumperchlorate absorbe light. 9. The novel composition of matter of claim 8wherein said cation is Ca.

10. The novel composition of matter of claim 8 wherein said cation isSr.

2. The process of claim 1 wherein said anion is SO4.
 3. A process fordecelerating the rate of thermal decomposition of nitronium perchloratecomprising cocrystallizing with it about 0.001 to about 20 mole percentof a foreign cation that a. has a valence state greater than one, b. isthermally stable at the temperature of decomposition of said nitroniumperchlorate, and c. does not absorb light at a wavelength shorter thanthe wavelength at which nitronium perchlorate absorbs light, and thecorresponding amount of an anion that a. has a valence state less thanthe valence state of said cation, and b. does not absorb light at awavelength shorter than the wavelength at which nitronium perchlorateabsorbs light.
 4. The process of claim 3 wherein said cation is Ca . 5.The process of claim 3 wherein said cation is Sr .
 6. The novelcomposition of matter comprising a nitronium perchlorate lattice havingin ionic distribution therein about 0.001 to about 20 mole percent of aforeign anion that is thermally stable at the temperature ofdecomposition of said nitronium perchlorate and that has a valence stategreater than one, and a corresponding amount of a cation having avalence less than the valence of said anion.
 7. The novel composition ofmatter of claim 6 wherein said anion is SO4 .
 8. The novel compositionof matter comprising a nitronium perchlorate lattice having in ionicdistribution therein about 0.001 to about 20 mole percent of a foreigncation that a. has a valence state greater than one, b. is thermallystable at the temperature of decomposition of said nitroniumperchlorate, and c. does not absorb light at a wavelength shorter thanthe wavelength at which nitronium perchlorate absorbs light, and thecorresponding amount of an anion that a. has a valence state less thanthe valence state of said cation, and b. does not absorb light at awavelength shorter than the wavelength at which nitronium perchlorateabsorbe light.
 9. The novel composition of matter of claim 8 whereinsaid cation is Ca .
 10. The novel composition of matter of claim 8wherein said cation is Sr .